The invention relates to a photosensitive color photographic silver halide material which contains, in at least one layer, at least one spectrally sensitized silver halide emulsion containing at least 95 mol-% AgCl, preferably at least 98.5 mol-% AgCl, and has improved low-density stability in the unexposed state (lower storage fog).
It is known that AgCl emulsions frequently have a high fog which is produced by reduction of silver ions to metallic silver during the precipitation. To avoid this, oxidizing agents such as Hg salts, permanganates, peroxides and persulfates are added. Said oxidizing agents frequently have a negative effect on the photographic properties, particularly on the sensitivity.
It is furthermore known that silver halide emulsions having a high chloride content exhibit a density increase in the region of the threshold gradation during storage, regardless of the spectral sensitivity. The heat stability of spectrally sensitized, in particular blue-sensitized, silver chloride emulsions is also unsatisfactory in the region of low densities.
The object of the invention was to avoid these disadvantageous effects.
It was found that the addition of salts of indium, of yttrium, of lanthanum and of the rare earths cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium, referred to below as earth-metal salts, to one of the solutions of the emulsion mixture for producing a photosensitive silver halide emulsion having a high chloride content results in an unexpected improvement in the fog in the fresh state and in the stability of the photographic properties during storage in the unexposed state, whereas the low densities (emulsion fog and threshold gradation) are essentially kept stable at elevated temperature.
Disadvantageous alterations in the photographic properties of the emulsions are not associated with the addition, according to the invention, of the earth-metal salts.
The addition of rare-earth-metal salts to silver halide emulsions has hitherto been disclosed (U.S. Pat. No. 3,178,289) only in connection with the improvement of the point quality in photographic emulsions containing at least 7.5 mol-% AgBr which are subjected to a lith development.
The doping of a silver halide emulsion whose grains have at least 4 shells, of which at least one shell, but not all the shells, are doped with indium or lanthanum and the like or another shell, but not all the shells are doped with iodine, results, in black/white materials, in a stabilization of the photographic properties (DE 37 23 419).
The invention consequently relates to a color photographic silver halide material having a base and at least one photosensitive silver halide emulsion layer which is applied thereto and whose silver halide comprises at least 95 mol-%, preferably at least of 98.5%, of AgCl, characterized in that the silver halide emulsion contains 10xe2x88x927 to 10xe2x88x923 mol of at least one metal selected from indium, yttrium, lanthanum and the lanthanides per mol of silver halide.
The silver halide crystals are preferably prismatic, cubic or tabular. They are, in particular, blue-sensitized.
The silver halide crystals according to the invention are prepared in that the silver halide precipitation is performed in the presence of soluble salts of metals of the lanthanide group, of indium or of yttrium or are redissolved with fine-grain silver halide crystals doped with the said metals.
According to the invention, the soluble simple or complex salts, including the halides, sulfates and nitrates of the bivalent, trivalent or tetravalent metals, in particular, are used as soluble earth metal salts.
The amount of halide of the silver halides required to make up to 100 mol-% is preferably AgBr.
The color photographic silver halide material is, in particular, a print material.
Preferably the following metal salts are used: Pr, Eu, Ce and In.
The emulsions according to the invention are ripened in the normal manner, stabilized, chemically and spectrally sensitized and mixed with the usual emulsion additives.
Suitable as ripening agents are, for example, thiosulfate, thiourea, open-chain and cyclic thioamides, thiocarbamates, xanthogenates, selenoureas, open-chain or cyclic selenoamides, heterocyclic, in particular heteroaromatic selenols, phosphane selenides, selenium sulfates, selenium phosphates, selenium phosphonates, selenium phosphoramides.
Preferred blue-sensitizers correspond to the formula (I) 
wherein
R11 to R13 and R16 to R18 represent H, alkyl, alkoxy, halogen, 2-thienyl, 3-thienyl, 1-pyrrolyl, 2-pyrrolyl, phenyl, 1-indolyl, 2-furanyl, 3-furanyl or carbazolyl,
R14 and R15 represent alkyl, sulfoalkyl, carboxyalkyl, xe2x80x94(CH2)nSO2Nxcex8xe2x80x94COR19, xe2x80x94(CH2)nSO2Nxcex8SO2R19, xe2x80x94(CH2)nCONxcex8SO2R19 or xe2x80x94(CH2)nCONxcex8COR19,
X11 and X12 represent O, S, Se, or NR20,
M represents a counterion,
n represents an integer from 2 to 4 and
R19 and R20 represent C1-C4-alkyl or
R11 and R12 or R12 and R13, R16 and R17 or R17 and R18 represent the remaining members of a fused benzene or naphthalene ring.
Particularly preferred blue-sensitizers correspond to the formula (II) 
wherein
R21 and R23 represent hydrogen
R22 represents halogen, in particular chlorine or fluorine, 2-thienyl, 3-thienyl, 1-pyrrolyl, 2-furanyl, 1-indolyl or phenyl or
R21 and R22 taken together or R22 and R23 taken together represent the remaining members of a fused benzene or naphthalene ring,
R24 represents hydrogen,
R25 represents halogen, in particular chlorine or fluorine, phenyl, 2-thienyl, 3-thienyl, 1-pyrrolyl, 2-furanyl, 1-indolyl or
R24 and R25 taken together represent the remaining members of a fused benzene or naphthalene ring,
X21 represents S or O,
M represents a counterion, in particular triethylamrnonium, and
l and m represent an integer from 2 to 4.
The blue-sensitized silver halide emulsion contains, in particular, a stabilizer selected from the 1-phenyl-5-mercaptotetrazoles.
The blue-sensitized silver halide emulsion layer normally contains at least one yellow-coupler, preferably a biequivalent yellow-coupler.
Preferred as two-equivalent yellow-couplers are acetanilides, in particular pivaloyl-acetanilides and malonanilides whose labile groups are linked via O or N with the coupler molecule and which are substituted in the ortho-position of the anilide part by chlorine, alkoxy or aryloxy.
Particularly preferred two-equivalent yellow couplers correspond to the formula (III): 
wherein
R31 represents alkyl, preferably containing 1 to 4 C atoms, in particular methyl,
R32 represents alkyl, preferably containing 1 to 4 C atoms, in particular methyl,
R33 represents a hydrogen atom or alkyl, preferably containing 1 to 4 C atoms, in particular methyl, or
R32 and R33 taken together represent the remaining members of a cyclopropyl radical,
R34 represents chlorine or alkoxy,
R35 represents xe2x80x94NHCOxe2x80x94R37, xe2x80x94SO2NHxe2x80x94R37, xe2x80x94NHSO2xe2x80x94R37, xe2x80x94COOR37, Cl, Br or alkoxy,
R36 represents a hydrogen or chlorine atom,
R37 represents a substituent, in particular a ballast group and
Q represents the remaining members of a substituted imidazole, imidazolidinedione, oxazolidinedione or triazolidinedione ring,
wherein the alkyl groups may be further substituted.
Suitable yellow couplers are 
Suitable compounds of the formula (II) are the following, in which 1 and m=3 and triethylammonium is counterion:
Examples of color photographic silver halide materials are color photographic paper, color-reversal photographic paper and semi-transparent display material. An overview is to be found in Research Disclosure 37038 (1995), Research Disclosure 38957 (1996) and Research Disclosure 40145 (1997).
The color photographic silver halide materials comprise a base to which at least one photosensitive silver halide emulsion layer is applied. Suitable bases are, in particular, thin films and sheets. An overview of base materials and auxiliary layers applied to their front and back sides is presented in Research Disclosure 37254, Part 1 (1995), page 285 and in Research Disclosure 38957, Part XV (1996), page 627.
The color photographic silver halide materials normally contain at least one red-sensitive, green-sensitive and blue-sensitive silver halide emulsion layer, respectively, and also, optionally, interlayers and protective layers.
Depending on the nature of the photographic silver halide materials, said layers may. be arranged differently. This may be explained for the most important products:
Color photograph paper and color photographic display material normally have on the base in the sequence specified below a blue-sensitive, yellow-coupling silver halide emulsion layer, a green-sensitive, magenta-coupling silver halide emulsion layer and a red-sensitive, cyan-coupling silver halide emulsion layer, respectively; a yellow filter layer is unnecessary.
Modifications may be made to the number and arrangement of the photosensitive layers to achieve certain results. For example, colour papers may also contain otherwise sensitized interlayers by means of which the gradation may be influenced.
Essential constituents of the photographic emulsion layers are binders, silver halide grains and colour couplers.
Details on suitable binders are to be found in Research Disclosure 37254, Part 2 (1995), page 286 and in Research Disclosure 38957, Part II.A (1996), page 598.
Details on suitable silver halide emulsions, their preparation, ripening, stabilization and spectral sensitization, including suitable spectral sensitizers, are to be found in Research Disclosure 37254, Part 3 (1995), page 286, in Research Disclosure 37038, Part XV (1995), page 89 and in Research Disclosure 38957, Part V.A (1996), page 603.
The spectral sensitizers can be added in dissolved form or as dispersed substances to the photographic emulsion. Both solution and dispersed substance may contain additives, such as wetting agents or buffers.
The spectral sensitizer or a combination of spectral sensitizers can be added before, during or after the preparation of the emulsion.
Details on colour couplers are to be found in Research Disclosure 37254, Part 4 (1995), page 288, in Research Disclosure 37038, Part II (1995), page 80 and in Research Disclosure 38957, Part X.B (1996), page 616. The maximum absorption of the dyestuffs formed from the couplers and the colour developer oxidation product is, for copying materials, preferably in the following ranges: yellow coupler 440 to 450 nm, magenta coupler 540 to 560 nm, cyan coupler 640 to 670 nm.
The usual magenta couplers in copier materials are almost exclusively those selected from the anilinopyrazolones, the pyrazolo[5.1-c](1,2,4)triazoles or the pyrazolo[1.5-b](1,2,4)triazoles.
The non-photosensitive interlayers disposed as a rule between layers of different spectral sensitivity may contain agents which prevent an undesirable diffusion of developer oxidation products out of one photosensitive layer into another photosensitive layer having different spectral sensitization.
Suitable compounds (white coupler, scavengers or EOP traps) are to be found in Research Disclosure 37254, Part 7 (1995), page 292, in Research Disclosure 37038, Part III (1995), page 84 and in Research Disclosure 38957, Part X.D (1996), page 621 ff.
The color photographic material may furthermore contain UV-absorbing compounds, white toners, spacers, filter dyes, formalin traps, light protection agents, antioxidants, Dmin dyes, plasticizers (latices), biocides and additives for improving the coupler and dye stability, for reducing the colour fog and for reducing the yellowing, etc. Suitable compounds are to be found in Research Disclosure 37254, Part 8 (1995), page 292, in Research Disclosure 37038, Parts IV, V, VI, VII, X, XI and XIII (1995), page 84 ff and in Research Disclosure 38957, Parts VI, VIII, IX and X (1996), page 607 and 610 ff.
The layers of color photographic materials are normally cured, i.e. the binder used, preferably gelatin, is crosslinked by suitable chemical methods.
Suitable curing substances are to be found in Research Disclosure 37254, Part 9 (1995), page 294, in Research Disclosure 37038, Part XII (1995), page 86 and in Research Disclosure 38957, Part II.B (1996), page 599.
After imagewise exposure, color photographic materials are processed by various methods in accordance with their nature. Details on the procedures and the chemicals needed therefor are published in Research Disclosure 37254, Part 10 (1995), page 94, in Research Disclosure 37038, Parts XVI to XXIII (1995), page 95 ff and in Research Disclosure 38957, Parts XVIII, XIX and XX (1996), page 630 ff together with exemplary materials.